Thanks for your reply. To answer your question, I have a very limiled experience with solid state circuits but for 32 years I worked on standby generators from 2.5 kw to 2 megwatt set, so I try to be very careful with all electrical work. As I stated in my first post I removed the motor controller from a used treadmill (it was free) and was able to get it in a box and up and working. Years ago I built a Heathkit fish finder and a couple of other small projects. So now I wanted to try my hand at a little better controller at 90v dc 18-20 amps. The new motor I have is rated at that, so here I am looking for plans or suggestion on where to look.